Causes of overweight and obesity

The root causes of overweight and obesity are varied and complex. Overweight and obesity mainly occurs when there is a sustained energy imbalance, where too much energy is consumed through food and drink, and not enough is expended through physical activity. However, many other factors also influence overweight and obesity, including:

  • Genetics/physiology (for example, metabolism, appetite, satiety and body fat distribution)
  • Health inequalities (for example, area of remoteness, socioeconomic disadvantage, ethnic/cultural groups)
  • Environmental factors (for example, availability of fast-food outlets, portion sizes, home and neighbourhood environments)
  • Commercial determinants (for example, media and advertising, retail environments).

Healthy eating and physical activity are important for a healthy, active life. Maintaining your weight means balancing the energy going into your body and the energy being used for growth and repair, for physical activity, and to keep your bodily functions working.

Food and nutrition

The total amount of food that your body needs depends on your age, sex, body size, level of physical activity and whether you are pregnant or breastfeeding. Children and adolescents need enough nutritious food to grow and develop normally. Older people need to eat nutritious foods to help maintain a healthy weight.

The body converts the protein, fat and carbohydrate in food to energy. Excess energy intake, even a small amount over a long period, will cause weight gain. Visit to calculate your individual energy requirements.

The Australian Guide to Healthy Eating is a food selection guide that visually represents the proportion of the five food groups recommended for consumption each day. Following these recommendations and limiting the number of energy-dense, nutrient-poor discretionary foods and drinks is the best way to maintain a healthy weight.

For more information, see Diet.

Physical activity

The human body expends energy in 3 ways:

  • Basal metabolism (the energy used to keep the body functioning at rest, such as breathing and blood circulation)
  • Thermic processes (the energy taken to digest and absorb food)
  • Physical activity (the energy used to move around).

Physical activity is the component a person has the most control over. Being physically active throughout life helps to promote health and wellbeing and prevent chronic disease. Not expending enough energy can contribute to weight gain and overweight or obesity (AIHW 2018b).

Too much sedentary behaviour (sitting or lying down, except when sleeping) can also contribute to overweight and obesity (AIHW 2018b). Australia’s Physical Activity and Sedentary Behaviour Guidelines recommend the type, duration, intensity and frequency of physical activity, and practices for sedentary behaviour, for people during different life stages.

For more information, see Physical activity.

Obesogenic environments

The term ‘obesogenic environment’ is used to describe an environment that promotes obesity (Swinburn, et al. 1999). Schools, workplaces, homes and neighbourhoods, the media, availability of convenience foods, and portion sizes can all influence a person’s body weight. See A picture of overweight and obesity in Australia for more information on obesogenic environments.